1. Field of the Invention
The present invention relates to a coaxial connector, and more particularly, to a coaxial connector for a coaxial cable. The coaxial cable preferably comprises a cylindrical metal thin film serving as an outer conductor and is generally intended to transmit a high frequency signal therethrough.
2. Description of the Related Art
In recent years, a coaxial cable has been developed to have a high quality in its band width and a high reliability and used in various technical fields, for example, a mobile telecommunication system, a video signal transmission system and so on. As described above, the coaxial cable of this type generally comprises a cylindrical metal thin film serving as an outer conductor and is adapted to transmit a high frequency signal therethrough.
For instance, the mobile telecommunication system includes a base station. In the base station, the system comprises an antenna, a band-pass filter and an amplifier. The antenna is adapted to receive a radio wave signal having a faint level. The amplifier is designed to amplify the signal which is passed through the band-pass filter. The coaxial cable is used for the electrical connection between the antenna, the band-pass filter and the amplifier.
Recently, the band-pass filter has been developed into a high efficient filter including a high temperature superconductor (hereinlater referred to as "HTS filter"). The HTS filter is generally accommodated in a refrigerated vacuum chamber and has the coaxial cable of the type above mentioned used for the electrical connection between the antenna and the amplifier.
The coaxial cable is generally used in conjunction with a coaxial connector for electrically and mechanically connecting one device to the other device therethrough. The coaxial connector has been also developed with the advance of high technology to have a high quality commensurate with that of the coaxial cable.
Referring to FIG. 4 of the drawings, there is shown a conventional coaxial connector 60 suitable for this type of coaxial cable 50. The coaxial cable 50 comprises a cylindrical inner conductor 51, a tubular dielectric member 52, and a tubular outer conductor 53. The inner conductor 51 is made of a conductive wire having a circular cross-section taken along a plane perpendicular to its longitudinal axis. The dielectric member 52 encircles and supports the inner conductor 51. The outer conductor 53 is made of a metal thin film having a predetermined thickness and covers the outer surface of the dielectric member 52. The coaxial cable 50 is electrically connected to some devices, not shown, at its both ends by way of respective coaxial connectors 60.
The coaxial connector 60 comprises a connector pin 61 electrically connected to the inner conductor 51 and having a center axis axially aligned with the center axis of the coaxial cable 50, a cylindrical connector body 62 electrically connected to the outer conductor 53, a cylindrical dielectric member 63 disposed between the connector pin 61 and the connector body 62, and an outer housing 65. The cylindrical connector body 62 is adapted to retain one end portion of the coaxial cable 50 and part of the connector pin 61. The cylindrical connector body 62 is welded to the outer conductor 53 of the coaxial cable 50 at a solder portion 71. The outer housing 65 is rotatably mounted around and in concentric and radially spaced relation with the cylindrical connector body 62 through a snap ring 64 so as to have the cylindrical connector body 62 to the coaxial cable 50 held at a standstill to each other.
The conventional coaxial connector 60 as described above and shown in FIG. 4, however, has a drawback to be encountered in its electrical property. In the coaxial connector 60, the thin film of the outer conductor 53 of the coaxial cable 50 is liable to be deformed or peel off from the dielectric member 52 of the coaxial cable 50 during a heating process to melt solder to connect the coaxial connector 60 to the coaxial cable 50 at the solder portion 71. The deformation or peeling of the outer conductor 53 of the coaxial cable 50 is also frequently caused at the end of the coaxial cable 50 near the coaxial connector 60 whenever the coaxial cable 50 is bent. These phenomena are apt to lead to a trouble that the electrical property of the coaxial connector 60 as well as the coaxial cable 50 is extremely deteriorated. Furthermore, it is difficult to form the solder portion 71 uniformly. As a result, some thermal shock causes cracks in an uneven portion of the solder portion 71.
The other type of coaxial connector for the coaxial cable, such as a collet chuck type of coaxial connector, is disclosed in U.S. patent application Ser. No. 821,294, filed Mar. 20, 1997, by the same applicant. The above type of coaxial connector comprises a clamp having the collet chuck type of structure instead of a solder portion for electrically and mechanically connecting the coaxial cable to the coaxial connector.
The coaxial connector of this type can be used for thin film coated coaxial cables thereby achieving a high performance of its electrical property and a high thermal conductivity. However, the coaxial connector of the collet chuck type generally has complex structures. For this reason, the coaxial connector cannot be reduced small in size and produced at a relatively low cost. The collet chuck type of coaxial connector further encounters a drawback in its insertion loss as described below. The collet chuck type of coaxial connector is generally applied to the coaxial cable coated with the metal thin film as described above. The coaxial connector for the thin film coated coaxial cable causes the high insertion loss in comparison with the coaxial connector for the semi-rigid type of coaxial cable.
The insertion losses of the cable and connector were measured in order to evaluate the coaxial connector for the thin film coated coaxial cable in comparison with that of the connector for the semi-rigid type of coaxial cable.
The measurements were conducted under the condition that the high frequency signal is transmitted though the connector and cable at a frequency of 5 GHz. The results of the measurements indicate that the insertion loss of the semi-rigid type of coaxial cable indicates 0.008 dB/cm while the insertion loss of the coaxial connector indicates 0.010 dB per one connector. In comparison with these results, the insertion loss of the thin film coated coaxial cable indicates 0.008 dB/cm which is the same as that of the semi-rigid type of coaxial cable while the insertion loss of the coaxial connector indicates 0.042 dB per one connector which is four times larger than that of the connector for the semi-rigid type of coaxial cable. From the foregoing it will be seen that the collet chuck type of coaxial connector has a disadvantage against the connector for the semi-rigid type of coaxial cable in its insertion loss when the coaxial connector is used for the thin film coated coaxial cable.
Furthermore, the other type of coaxial connector comprising a ferrule which is adapted to connect the cable to the connector therethrough is disclosed in Japanese laid-opened Publication No. 01-130485 (Kauffman; Roger S.) corresponding to U.S. patent application Ser. No. 112,910, filed Oct. 23, 1987.